Cooling and heating system

ABSTRACT

There is disclosed a cooling and heating system in which a refrigerant is used in a supercritical state and in which cooling and heating capacity can be controlled so as to maximize a coefficient of performance. A cooling and heating system  130  includes: an outdoor unit  101  indicating a compressor  102  and an outdoor heat exchanger  103   a ; a plurality of indoor units  105  including indoor heat exchangers  106 ; a high pressure tube  111 ; a low pressure tube  112 ; and an intermediate tube  113 . The system includes: a refrigerant pressure detection unit P C01  for measuring a pressure of the refrigerant discharged from the compressor  102 ; a first refrigerant temperature detection unit T C03  which measures an outlet temperature of the refrigerant in a case where the outdoor heat exchanger  103  functions as a gas cooler and which measures an inlet temperature of the refrigerant in a case where the outdoor heat exchanger  103  functions as an evaporator; and a second refrigerant temperature detection unit T CO8  which measures an outlet temperature of the refrigerant in a case where the indoor heat exchanger  106  functions as a gas cooler and which measures an inlet temperature of the refrigerant in a case where the indoor heat exchanger  106  functions as an evaporator.

BACKGROUND OF THE INVENTION

The present invention relates to a cooling and heating system, more particularly to a cooling and heating system which uses a refrigerant in a supercritical state and which can control cooling and heating capacity so as to maximize a coefficient of performance.

A cooling and heating system described in Japanese Patent Application Laid-Open No. 2004-226018 is known as a cooling and heating system in which a carbon dioxide refrigerant is used in a supercritical state. The system has an outdoor unit and a plurality of indoor units, the plurality of indoor units can be operated at the same time in a cooling operation or a heating operation, and the cooling operation and the heating operation can be performed in a mixed manner. Here, the cooling operation refers to an operation to be performed in a case where a set temperature of the indoor unit is lower than an indoor temperature, and the heating operation refers to an operation to be performed in a case where the set temperature of the indoor unit is higher than the indoor temperature.

When a fluorocarbon refrigerant is used in the cooling and heating system, an evaporation temperature (or an evaporation pressure) or a condensation temperature (or a condensation pressure) is measured to grasp a state of the refrigerant. Capacities of a heat exchanger in the indoor unit and a compressor are controlled so that a measured value of the temperature comes close to a target value (a coefficient of performance is maximized). Here, the capacity control of the heat exchanger in the outdoor unit indicates that: a plurality of heat exchangers having different sizes are connected depending on a heat balance between a cooling load and a heating load on an indoor side, the heat exchangers are provided with change valves, respectively, and the number of the heat exchangers to be operated is changed; an amount of the refrigerant to be circulated in each heat exchanger is adjusted; or a rotational speed of a blower disposed in each heat exchanger is adjusted to control the capacity so that the temperature reaches the targeted evaporation or condensation temperature.

On the other hand, in the cooling and heating system in which a refrigerant such as carbon dioxide is used in a supercritical state, a high pressure side has a supercritical state. Therefore, there is a problem that the condensation pressure (high pressure) cannot be uniquely obtained from the condensation temperature (this refers to a high-pressure-side temperature because condensation does not occur in actual) unlike the fluorocarbon refrigerant, and both of the condensation temperature and the condensation pressure have to be measured on the high pressure side in order to grasp the state of the refrigerant. Therefore, it has been difficult to control the capacities of the heat exchanger and the compressor so as to maximize the coefficient of performance.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a cooling and heating system in which cooling and heating capacity can be controlled so as to maximize a coefficient of performance and in which a refrigerant is used in a supercritical state.

The present invention has been developed in order to achieve the above-described object. In a first aspect of the present invention, there is provided a cooling and heating system including: an outdoor unit including a compressor and an outdoor heat exchanger; and a plurality of indoor units including indoor heat exchangers and connected to one another by a pipe between the units, one end of the outdoor heat exchanger being selectively connected to a refrigerant discharge tube and a refrigerant suction tube of the compressor, the pipe between the units including: a high pressure tube connected to the refrigerant discharge tube; a low pressure tube connected to the refrigerant suction tube; and an intermediate pressure tube connected to the other end of the outdoor heat exchanger, one end of the indoor heat exchanger of each indoor unit being selectively connected to the high pressure tube and the low pressure tube, the other end of the indoor heat exchanger being connected to the intermediate pressure tube, the plurality of indoor units being simultaneously allowed to perform a cooling operation or a heating operation or the plurality of indoor units being allowed to perform a cooling operation and a heating operation simultaneously in a mixed manner, the cooling and heating system comprising: refrigerant pressure measurement means for measuring a pressure of the refrigerant discharged from the compressor; first refrigerant temperature measurement means which is disposed in the outdoor unit and which measures an outlet temperature of the refrigerant in a case where the outdoor heat exchanger functions as a gas cooler and which measures an inlet temperature of the refrigerant in a case where the outdoor heat exchanger functions as an evaporator; and second refrigerant temperature measurement means which is disposed in the indoor unit and which measures an outlet temperature of the refrigerant in a case where the indoor heat exchanger functions as a gas cooler and which measures an inlet temperature of the refrigerant in a case where the indoor heat exchanger functions as an evaporator.

Moreover, in a second aspect of the present invention, there is provided a cooling and heating system including: an outdoor unit including a compressor and an outdoor heat exchanger; and a plurality of indoor units including indoor heat exchangers and connected to one another by a pipe between the units, one end of the outdoor heat exchanger being selectively connected to a refrigerant discharge tube and a refrigerant suction tube of the compressor, the pipe between the units including: a high pressure tube connected to the refrigerant discharge tube; a low pressure tube connected to the refrigerant suction tube; and an intermediate pressure tube connected to the other end of the outdoor heat exchanger, one end of the indoor heat exchanger of each indoor unit being selectively connected to the high pressure tube and the low pressure tube, the other end of the indoor heat exchanger being connected to the intermediate pressure tube, the plurality of indoor units being simultaneously allowed to perform a cooling operation or a heating operation or the plurality of indoor units being allowed to perform a cooling operation and a heating operation simultaneously in a mixed manner, the cooling and heating system comprising: discharge temperature measurement means for measuring a temperature of the refrigerant discharged from the compressor; first refrigerant temperature measurement means which is disposed in the outdoor unit and which measures an outlet temperature of the refrigerant in a case where the outdoor heat exchanger functions as a gas cooler and which measures an inlet temperature of the refrigerant in a case where the outdoor heat exchanger functions as an evaporator; and second refrigerant temperature measurement means which is disposed in the indoor unit and which measures an outlet temperature of the refrigerant in a case where the indoor heat exchanger functions as a gas cooler and which measures an inlet temperature of the refrigerant in a case where the indoor heat exchanger functions as an evaporator.

Furthermore, in a third aspect of the present invention, in the cooling and heating system of the first or second aspect, the high side pressure of the refrigeration cycle is above the critical pressure of the refrigerant during the operation of the cooling and heating system. In a fourth aspect of the present invention, in the cooling and heating system of the third aspect, carbon dioxide is used as the refrigerant.

According to the present invention, in the cooling and heating system in which the refrigerant is used in the supercritical state, cooling and heating capacity can be controlled so as to maximize a coefficient of performance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing a cooling and heating system of the present invention;

FIG. 2 is a P-h diagram showing a refrigeration cycle of the cooling and heating system in the present invention;

FIG. 3 is a control flowchart for determining an operation mode of an outdoor heat exchanger in the cooling and heating system of the present invention;

FIG. 4 is a control flowchart of thermal load balance control in Embodiment 1 of the present invention;

FIG. 5 is a schematic diagram showing the cooling and heating system in Embodiment 1 of the present invention;

FIG. 6 is a control map diagram at a time when the outdoor heat exchanger is an evaporator in Embodiment 1 of the present invention;

FIG. 7 is a control map diagram at a time when the outdoor heat exchanger is a gas cooler in Embodiment 1 of the present invention;

FIG. 8 is a control flowchart of thermal load balance control in Embodiment 2 of the present invention;

FIG. 9 is a schematic diagram showing the cooling and heating system in Embodiment 2 of the present invention;

FIG. 10 is a control map diagram at a time when the outdoor heat exchanger is an evaporator in Embodiment 2 of the present invention; and

FIG. 11 is a control map diagram at a time when the outdoor heat exchanger is a gas cooler in Embodiment 2 of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 is a schematic diagram of a cooling and heating system of the present invention. This cooling and heating system 30 includes: an out door unit 1 including outdoor heat exchangers 3 a, 3 b and outdoor expansion valves 27 a, 27 b; an indoor unit 5 a including an indoor heat exchanger 6 a and an indoor expansion valve 18 a; an indoor unit 5 b including an indoor heat exchanger 6 b and an indoor expansion valve 18 b; and a hot water unit 50 including a gas cooler 41, a hot water storage tank 43, a circulation pump 45, and a circulation valve 47. Moreover, the out door unit 1, the indoor units 5 a, 5 b, and the hot water unit 50 are connected to one another by inter-unit piping 10. While operating the hot water unit 50, the cooling and heating system 30 simultaneously allows the indoor units 5 a, 5 b to perform a cooling operation or a heating operation. Alternatively, the cooling operation and the heating operation can be performed in a mixed manner.

In the out door unit 1, ends of the indoor heat exchangers 3 a, 3 b are selectively connected to a discharge tube 7 and a suction tube 8 of the compressor 2 via change valves 9 a and 9 b, and 19 a and 19 b, respectively. The suction tube 8 is provided with an accumulator 4. The out door unit 1 includes an outdoor control device (not shown), and this outdoor control device controls the compressor 2 in the out door unit 1, the outdoor expansion valves 27 a, 27 b, the change valves 9 a, 9 b, 19 a, and 19 b, and the cooling and heating system 30. The inter-unit piping 10 includes a high-pressure gas tube 11, a low-pressure gas tube 12, and a liquid tube 13. The high-pressure gas tube 11 is connected to the discharge tube 7, and the low-pressure gas tube 12 is connected to the suction tube 8. The liquid tube 13 is connected to the other ends of the outdoor heat exchangers 3 a, 3 b via the outdoor expansion valves 27 a, 27 b.

Ends of the indoor heat exchangers 6 a, 6 b of the indoor units 5 a, 5 b are connected to the high-pressure gas tube 11 via discharge-side valves 16 a, 16 b, and connected to the low-pressure gas tube 12 via suction-side valves 17 a, 17 b. The other ends of the indoor heat exchangers are connected to the liquid tube 13 via the indoor expansion valves 18 a, 18 b, respectively. When one of the discharge-side valve 16 a and the suction-side valve 17 a is opened, the other valve is closed. Similarly, when one of the discharge-side valve 16 b and the suction-side valve 17 b is opened, the other valve is closed. This selectively connects the ends of the indoor heat exchangers 6 a, 6 b to the high-pressure gas tube 11 and the low-pressure gas tube 12 of the inter-unit piping 10. The indoor units 5 a, 5 b further have indoor fans 23 a, 23 b, remote controllers (not shown), and indoor control devices. The indoor fans 23 a, 23 b are disposed close to the indoor heat exchangers 6 a, 6 b to send air to the indoor heat exchangers 6 a, 6 b, respectively. The remote controllers are connected to the indoor units 5 a, 5 b, respectively, and output cooling or heating operation commands, stop commands or the like to the indoor control devices, respectively.

In the hot water unit 50, one end of the gas cooler 41 is connected to the high-pressure gas tube 11, and the other end of the gas cooler 41 is connected to the liquid tube 13 via the circulation valve 47. This gas cooler 41 is connected to a water pipe 46, and this water pipe 46 is connected to the hot water storage tank 43 via the circulation pump 45.

In the present embodiment, a carbon dioxide refrigerant is introduced into the out door unit 1, the indoor units 5 a, 5 b, the hot water unit 50, and the inter-unit piping 10. In a case where the carbon dioxide refrigerant is introduced, as shown in an enthalpy and pressure (P-h) graph, the high side pressure of the refrigeration cycle, such as the pressure in the high-pressure gas tube 11 is a supercritical pressure. As to a refrigerant for use in the trance critical refrigeration cycle, examples of the refrigerant include ethylene, diborane, ethane, and nitrogen oxide.

In FIG. 2, an outlet of the compressor 2 in a state a. The refrigerant circulates through the heat exchanger (gas cooler), rejects heat, and is cooled to a state b. Moreover, the refrigerant reaches a state c owing to a pressure drop in the expansion valve (throttling device) to form a two-phase mixture of gas and liquid. In the heat exchanger (evaporator), heat is absorbed by evaporation of a liquid phase, and a state d is brought in an outlet of the evaporator. Moreover, the refrigerant flows toward the suction tube 8 of the compressor 2. In the present embodiment, since a two-stage compressor is used in the compressor 2, a folded line is drawn between the states d and a.

Next, an operation of the cooling and heating system 30 will be described.

In this cooling and heating system 30, the refrigerant discharged from the compressor 2 is introduced into the gas cooler 41 through the high-pressure gas tube 11, this gas cooler 41 heats water passing through the water pipe 46, and water at high temperature is stored in the hot water storage tank 43 (hot-water storage operation). Since the carbon dioxide refrigerant is used, and a high-pressure supercritical cycle is obtained, water is stored at a high temperature of about 80° C. or more in the tank. Moreover, hot water stored in this hot water storage tank 43 is sent to various hot-water facilities such as a bathroom, kitchen, and floor heating via piping (not shown).

In a case where the cooling operation is simultaneously performed by all of the indoor units 5 a, 5 b, the change valves 9 a, 9 b of the outdoor heat exchangers 3 a, 3 b are opened, the change valves 19 a, 19 b are closed, the discharge-side valves 16 a, 16 b are closed, and the suction-side valves 17 a, 17 b are opened. Accordingly, the refrigerant discharged from the compressor 2 successively flows to the discharge tube 7, the change valves 9 a, 9 b, and the outdoor heat exchangers 3 a, 3 b. After the refrigerant exchanges heat (rejects heat) in the outdoor heat exchangers 3 a, 3 b, the refrigerant is distributed to the indoor expansion valves 18 a, 18 b of the indoor units 5 a, 5 b via the liquid tube 13, and the pressure of the refrigerant is reduced. Moreover, the refrigerant evaporates (absorbs heat) in the indoor heat exchangers 6 a, 6 b, and flows through the suction-side valves 17 a, 17 b. The refrigerant is successively passed through the low-pressure gas tube 12, the suction tube 8, and the accumulator 4, and sucked into the compressor 2. In this manner, all of the indoor units 5 a, 5 b are simultaneously cooled by functions of the indoor heat exchangers 6 a, 6 b functioning as evaporators, respectively (cooling operation).

Conversely, in a case where all of the indoor units 5 a, 5 b are simultaneously heated, the change valves 9 a, 9 b of the outdoor heat exchangers 3 a, 3 b are closed, the change valves 19 a, 19 b are opened, the discharge-side valves 16 a, 16 b are opened, and the suction-side valves 17 a, 17 b are closed. Accordingly, the refrigerant discharged from the compressor 2 is successively passed through the discharge tube 7 and the high-pressure gas tube 11 to flow to the discharge-side valves 16 a, 16 b and the indoor heat exchangers 6 a, 6 b. The refrigerant exchanges heat (rejects heat), and flows into the liquid tube 13. Moreover, the pressure of the refrigerant is reduced by the outdoor expansion valves 27 a, 27 b. The refrigerant evaporates (absorbs heat) in the outdoor heat exchangers 3 a, 3 b, and is thereafter successively passed through the change valves 9 a, 9 b, the suction tube 8, and the accumulator 4. The refrigerant is sucked into the compressor 2. All of the indoor units 5 a, 5 b are simultaneously heated by functions of the indoor heat exchangers 6 a, 6 b which function as gas coolers in this manner (heating operation).

Moreover, in a cooling/heating mixed operation in which, for example, the indoor unit 5 a is cooled, and simultaneously the indoor unit 5 b is heated, in accordance with a control flow (A1) of an outdoor unit operation mode shown in FIG. 3, a demanded load in each indoor unit is calculated (S14), and it is judged by a total load value (S15) whether the outdoor heat exchanger 3 is operated as a gas cooler or an evaporator (S16).

In a case where the outdoor heat exchanger 3 is operated as the gas cooler (S16N), the change valve 9 of the outdoor heat exchanger 3 is opened, and the change valve 19 is closed. Moreover, the discharge-side valve 16 a of the indoor unit 5 a and the suction-side valve 17 b of the indoor unit 5 b are closed, and the suction-side valve 17 a of the indoor unit 5 a and the discharge-side valve 16 b of the indoor unit 5 b are opened. Accordingly, the refrigerant discharged from the compressor 2 successively flows to the discharge tube 7, the change valve 9, the discharge-side valve 16 b of the indoor unit 5 b, the outdoor heat exchanger 3, and the indoor heat exchanger 6 b. After the refrigerant exchanges heat (rejects heat) in the outdoor heat exchanger 3 and the indoor heat exchanger 6 b, the refrigerant flows into the liquid tube 13 to enter the indoor expansion valve 18 a, and the pressure of the refrigerant is reduced in the valve. Moreover, the refrigerant evaporates (absorbs heat) in the indoor heat exchanger 6 a. After the refrigerant flows in the suction-side valve 17 a, the refrigerant is successively passed through the low-pressure gas tube 12, the suction tube 8, and the accumulator 4, and sucked into the compressor 2.

On the other hand, in a case where the outdoor heat exchanger 3 is operated as the evaporator (S16Y), the change valve 9 of the outdoor heat exchanger 3 is closed, and the change valve 19 is opened. Moreover, the discharge-side valve 16 a of the indoor unit 5 a and the suction-side valve 17 b of the indoor unit 5 b are closed, and the suction-side valve 17 a of the indoor unit 5 a and the discharge-side valve 16 b of the indoor unit 5 b are opened. Accordingly, the refrigerant discharged from the compressor 2 successively flows to the discharge tube 7, the discharge-side valve 16 b of the indoor unit 5 b, and the indoor heat exchanger 6 b. After the refrigerant exchanges heat (rejects heat) in this indoor heat exchanger 6 b, the refrigerant passes through the liquid tube 13, and is distributed to the outdoor expansion valve 27 and the indoor expansion valve 18 a. The pressure of the refrigerant is reduced in the valves. Moreover, the refrigerant evaporates (absorbs heat) in the outdoor heat exchanger 3 and the indoor heat exchanger 6 a. After the refrigerant flows through the change valve 19 and the suction-side valve 17 a, the refrigerant successively flows through the low-pressure gas tube 12, the suction tube 8, and the accumulator 4, and is sucked into the compressor 2.

Moreover, in a case where the hot water storage operation is simultaneously required, the total load value may be calculated assuming that a load of the hot water unit 50 is similar to that of the heating operation of the indoor unit 5.

As described above, during the cooling and heating mixed operation, or during the hot water storage operation, the refrigerant circulates so that the indoor heat exchanger, the outdoor heat exchanger, and a gas cooler are mutually, so-called thermally balanced. This makes possible an operation in which indoor heat and outdoor heat are efficiently utilized. Especially, during the mixed operation of the cooling operation by the indoor unit and the hot water storage operation, hot water can be stored (supplied) by indoor heat. Therefore, heat is remarkably effectively utilized. There is an effect of preventing a heat island phenomenon caused by heat rejection from the outdoor unit. Moreover, in a case where a supercritical cycle is set using carbon dioxide in the refrigerant, since high-pressure single-phase refrigerant vapor discharged from the compressor 2 does not condense in the high-pressure gas tube 11, unlike the Freon refrigerant, a disadvantage that the refrigerant liquefies and accumulated in the high-pressure gas tube 11 is solved. This obviates a necessity for a bypass tube or the like between the high-pressure gas tube 11 and the low-pressure gas tube 12, which has been required for recovering the accumulated refrigerant. The refrigerant can be prevented from accumulating in the high-pressure gas tube 11 without complicating any pipe structure. Furthermore, since any bypass tube or the like is not required, an electromagnetic valve used herein is not required, the control is not required, and cost is reduced.

There will be described hereinafter an embodiment for controlling the above-described operation of the cooling and heating system 30 so as to maximize a coefficient of performance.

Embodiment 1

In the present embodiment, there will be described an operation control by a high pressure and an evaporation temperature with reference to FIGS. 4, 5, 6, and 7.

First in the present embodiment, as shown in a control flow (B1) of a thermal load balance control of FIG. 4, an evaporation temperature T_(EVA) is measured (S150). A place to be measured differs with an operation state of a cooling and heating system 130. When the state c shown in FIG. 2 advances to the state d, a temperature during phase change of the refrigerant (carbon dioxide) from a liquid to a gas is the evaporation temperature T_(EVA). At this time, since the evaporation temperature T_(EVA) and an evaporation pressure P_(EVA) are uniquely determined, an object to be measured may be the evaporation pressure P_(EVA).

Next, an outlet refrigerant temperature T_(GC) of the gas cooler is measured. Here, if the heating operation is performed in an out door unit 105 a shown in FIG. 5 (S151), the outlet refrigerant temperature of an indoor heat exchanger 106 a is measured as T_(GC) (S152Y) by a temperature sensor T_(C08). Unless the heating operation is performed in both of the out door unit 105 a and an out door unit 105 b (S151), the outlet refrigerant temperature of an outdoor heat exchanger 103 a (it is assumed that the outdoor heat exchanger 103 a is used in preference to an outdoor heat exchanger 103 b) is measured as T_(GC) (S152N) by a temperature sensor T_(CO3). Here, the outlet refrigerant temperature of the indoor heat exchanger or the outdoor heat exchanger may be replaced with a temperature of environment in a place where the heat exchanger is installed (indoor temperature or outside air temperature).

Moreover, a target high pressure P_(H.OPT) is set from the measured evaporation temperature T_(EVA) and the outlet refrigerant temperature T_(GC) of the gas cooler (S153), and a high pressure P_(H) is measured (S154). A pressure sensor P_(C01) is disposed in the vicinity of an outlet of a compressor 102 to measure the high pressure P_(H).

A control operation is determined depending on states of the measured evaporation temperature T_(EVA) and high pressure P_(H) with respect to a predetermined reference temperature T_(S) and the target high pressure P_(H.OPT). In this case, when the outdoor heat exchanger 103 is operated as an evaporator (S155), in accordance with a thermal load balance control map (B2) shown in FIG. 6 (S156Y), the compressor 102 and the outdoor heat exchanger 103 are controlled (S157, S158). When the outdoor heat exchanger 103 is not operated as the evaporator (S155), in accordance with a thermal load balance control map (B3) shown in FIG. 7 (S156N), the compressor 102 and the outdoor heat exchanger 103 are controlled (S157, S158).

Embodiment 2

In the present embodiment, there will be described an operation control by a discharge temperature and an evaporation temperature with reference to FIGS. 8, 9, 10, and 11.

First in the present embodiment, as shown in a control flow (C1) of a thermal load balance control of FIG. 8, an evaporation temperature T_(EVA) is measured (S250). A place to be measured differs with an operation state of a cooling and heating system 230. When the state c shown in FIG. 2 advances to the state d, a temperature during phase change of the refrigerant (carbon dioxide) from a liquid to a gas is the evaporation temperature T_(EVA). At this time, since the evaporation temperature T_(EVA) and an evaporation pressure P_(EVA) are uniquely determined, an object to be measured may be the evaporation pressure P_(EVA).

Next, an outlet refrigerant temperature T_(GC) of the gas cooler is measured (S252). Here, if the heating operation is performed in an indoor unit 205 a shown in FIG. 9 (S251), the outlet refrigerant temperature of an indoor heat exchanger 206 a is measured as T_(GC) (S252Y) by a temperature sensor T_(C28). Unless the heating operation is performed in both of the indoor unit 205 a and an indoor unit 205 b (S251), the outlet refrigerant temperature of an outdoor heat exchanger 203 a (it is assumed that the outdoor heat exchanger 203 a is used in preference to an outdoor heat exchanger 203 b) is measured as T_(GC) (S252N) by a temperature sensor T_(C23). Here, the outlet refrigerant temperature of the indoor heat exchanger or the outdoor heat exchanger may be replaced with a temperature of environment in a place where the heat exchanger is installed (indoor temperature or outside air temperature).

Moreover, an optimum high pressure P_(H.OPT) is calculated from the measured evaporation temperature T_(EVA) and an outlet refrigerant temperature T_(GC) of the gas cooler, and a target discharge temperature T_(DIS.OPT) is set from the calculated optimum high pressure P_(H.OPT), and characteristics or a suction state of a compressor 202 (S253), and a discharge temperature T_(DIS) is measured (S254). A pressure sensor T_(C21) is disposed in the vicinity of an outlet of the compressor 202 to measure the discharge temperature T_(DIS).

A control operation is determined depending on states of the measured evaporation temperature T_(EVA) and discharge temperature T_(DIS) with respect to a predetermined reference temperature T_(S) and the target discharge temperature T_(DIS.OPT). In this case, when the outdoor heat exchanger 203 is operated as an evaporator (S255), in accordance with a thermal load balance control map (C2) shown in FIG. 10 (S256Y), the compressor 202 and the outdoor heat exchanger 203 are controlled (S257, S258). When the outdoor heat exchanger 203 is not operated as the evaporator (S255), in accordance with a thermal load balance control map (C3) shown in FIG. 11 (S256N), the compressor 202 and the outdoor heat exchanger 203 are controlled (S257, S258).

The present invention can be utilized in not only a cooling and heating system for business in a building or the like but also a household cooling and heating system having a hot water supply system or a floor heating system. 

1. A cooling and heating system including: an outdoor unit including a compressor and an outdoor heat exchanger; and a plurality of indoor units including indoor heat exchangers and connected to one another by a pipe between the units, one end of the outdoor heat exchanger being selectively connected to a refrigerant discharge tube and a refrigerant suction tube of the compressor, the pipe between the units including: a high pressure tube connected to the refrigerant discharge tube; a low pressure tube connected to the refrigerant suction tube; and an intermediate pressure tube connected to the other end of the outdoor heat exchanger, one end of the indoor heat exchanger of each indoor unit being selectively connected to the high pressure tube and the low pressure tube, the other end of the indoor heat exchanger being connected to the intermediate pressure tube, the plurality of indoor units being simultaneously allowed to perform a cooling operation or a heating operation or the plurality of indoor units being allowed to perform a cooling operation and a heating operation simultaneously in a mixed manner, the cooling and heating system comprising: refrigerant pressure measurement means for measuring a pressure of the refrigerant discharged from the compressor; first refrigerant temperature measurement means which is disposed in the outdoor unit and which measures an outlet temperature of the refrigerant in a case where the outdoor heat exchanger functions as a gas cooler and which measures an inlet temperature of the refrigerant in a case where the outdoor heat exchanger functions as an evaporator; and second refrigerant temperature measurement means which is disposed in the indoor unit and which measures an outlet temperature of the refrigerant in a case where the indoor heat exchanger functions as a gas cooler and which measures an inlet temperature of the refrigerant in a case where the indoor heat exchanger functions as an evaporator.
 2. A cooling and heating system including: an outdoor unit including a compressor and an outdoor heat exchanger; and a plurality of indoor units including indoor heat exchangers and connected to one another by a pipe between the units, one end of the outdoor heat exchanger being selectively connected to a refrigerant discharge tube and a refrigerant suction tube of the compressor, the pipe between the units including: a high pressure tube connected to the refrigerant discharge tube; a low pressure tube connected to the refrigerant suction tube; and an intermediate pressure tube connected to the other end of the outdoor heat exchanger, one end of the indoor heat exchanger of each indoor unit being selectively connected to the high pressure tube and the low pressure tube, the other end of the indoor heat exchanger being connected to the intermediate pressure tube, the plurality of indoor units being simultaneously allowed to perform a cooling operation or a heating operation or the plurality of indoor units being allowed to perform a cooling operation and a heating operation simultaneously in a mixed manner, the cooling and heating system comprising: discharge temperature measurement means for measuring a temperature of the refrigerant discharged from the compressor; first refrigerant temperature measurement means which is disposed in the outdoor unit and which measures an outlet temperature of the refrigerant in a case where the outdoor heat exchanger functions as a gas cooler and which measures an inlet temperature of the refrigerant in a case where the outdoor heat exchanger functions as an evaporator; and second refrigerant temperature measurement means which is disposed in the indoor unit and which measures an outlet temperature of the refrigerant in a case where the indoor heat exchanger functions as a gas cooler and which measures an inlet temperature of the refrigerant in a case where the indoor heat exchanger functions as an evaporator.
 3. The cooling and heating system according to claim 1 or 2, wherein the high side pressure of the refrigeration cycle is above the critical pressure of the refrigerant during the operation of the cooling and heating system.
 4. The cooling and heating system according to claim 3, wherein carbon dioxide is used as the refrigerant. 